1. Field of the Invention
This invention relates to apparatus for developing an electrostatic latent image formed on an image carrying substance with a dry developer by means of a magnetic brush development, and particularly to a developing apparatus using a magnetic toner of a one-component system as a dry developer.
2. Description of the Prior Art
In the fields of electronic photography, electrostatic recording and electrostatic printing, an electric latent image is formed on an image carrying substance and then developed by a magnetic brushing method using a magnetic developer, and the toner image thus developed is directly fixed on the image carrying substance or transferred normally to a sheet of paper or the like and then fixed thereon as a final image. As the image carrying substance, there are known an inorganic photoconductive material such as a photo-conductive selenium or a photosensitive material formed by dispersing photoconductive zinc oxide in an insulating resin binder, and an organic photoconductive material such as polyvinylcarbazole or poly-N-vinylcarbazole. These materials are used for electronic photograph copying machines and printers. Another known image carrying substance is an electrostatic recording paper having a dielectric layer mainly of an insulating resin formed on the conductive base paper, which is used in facsimile. The electric latent image in this invention includes electrostatic latent image, capacitive pattern, and conductive pattern, and the word "electrostatic latent image" containing them is used in the following description.
When an electrostatic latent image is developed by a magnetic brushing method, a mixture of ferromagnetic carrier particles and toner particles has been used as a magnetic developer. This ferromagnetic carrier particle is a core substance of iron powder, steel ball, ferrite powder, or the like, covered with a resin. The toner particle is formed by dispersing a coloring agent, such as pigment or dye, in a binder resin. Such a so-called two-component developing agent is used in a magnetic-brush type developing apparatus which, for example, is disclosed in the U.S. Pat. No. 3,697,050 (Stanly), or U.S. Pat. No. 3,703,395 (Drexler).
However, a one-component system magnetic toner has recently been used as a magnetic developing agent in the magnetic brush development, because it is unnecessary with such a one-component system magnetic toner to mix the carrier particles and toner particles, control the toner concentration in the developing agent, and interchange carrier particles. This magnetic toner, as, for example, disclosed in U.S. Pat. No. 3,639,245 (Nelson), U.S. Pat. No. 3,925,219 (Strong), and U.S. Pat. No. 4,189,390 (Mukon et al), contains chiefly a binder resin, and magnetic particles, and as necessary, added with an additive such as a conductive material, or a dye.
An apparatus for developing an electrostatic latent image using such a one-component magnetic toner, is, for example, disclosed in U.S. Pat. No. 4,021,571 (Nishihama et al), and, U.S. Pat. No. 4,231,370 (Asanae et al). In the example of Nishihama et al, a developing roll having a cylindrical non-magnetic sleeve and a cylindrical permanent magnet member provided in the sleeve is disposed to oppose a photosensitive material, and above the developing roll is disposed a toner bath with magnetic toner placed therein through its opening provided at its lower portion. In the example of Asanae et al, the developing roll disposed to oppose the photosensitive material is provided in the toner bath.
In these developing apparatuses, when the magnetic toner is supplied to the toner bath, the toner is generally poured therein by taking by hand a bottle or container of toner. However, this way of supplying toner will easily cause scattering of the toner and be difficult to supply constant toner to the toner bath. Thus, it is considered that a toner supply bath is provided in addition to the toner bath, and the container with toner is inserted into the toner supply bath to supply toner thereto, the toner within the toner supply bath being automatically supplied by the weight itself to the toner bath. In this case, however, after toner is filled in the toner bath, pressure in still exerted on the toner within the toner bath, and may cause the toner to be overflowed from the toner bath.
In U.S. Pat. No. 4,240,487 (Terashima et al), although means for detecting the amount of toner within the toner bath provided above the developing roll is included in the developing apparatus, no separate bath corresponding to the toner supply bath, from the toner bath is provided in this developing apparatus.